Myoclonus UMLS:C0027066 UMLS:C1854302 Myoclonus may be synchronous (several muscle contracting simultaneously), spreading (several muscles contracting in sequence), or asynchronous (several muscles contracting with varying and unpredictable relative timing). Myoclonus is characterized by sudden unidirectional movement due to muscle contraction (positive myoclonus) or due to sudden brief muscle relaxation (negative myoclonus). Electrophysiological tests are very helpful in determining whether myoclonus is cortical, subcortical or spinal. Very brief, involuntary random muscular contractions occurring at rest, in response to sensory stimuli, or accompanying voluntary movements. HP:0007087 Jerking SNOMEDCT_US:127324008 HP:0001336 SNOMEDCT_US:17450006 Myoclonic jerks Involuntary jerking movements HP:0002535 Involuntary movements